Bulk composition and mineral parageneses of sapphirine-bearing rocks along a gabbro-lherzolite contact at Finero, Ivrea Zone, N Italy |
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| Authors: | JANE D SILLS DIETRICH ACKERMAND RICHARD K HERD BRIAN F WINDLEY |
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| Institution: | Department of Geology, The University, Leicester LE1 7RH, UK; Mineralogisches Institut der Universität, D-2300 Kiel, FRG; Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A OE8; Department of Geology, The University, Leicester LE1 7RH, UK |
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| Abstract: | Sapphirine occurs in a 3-5 m wide zone between amphibole-lherzolite and garnetiferous metagabbro at Finero in the Ivrea Zone, NW Italian Alps. Layers consisting of plag + hb + sa + cpx + opx + sp + gt are interbanded with spinel pyroxenites, which may contain sapphirine replacing spinel. All minerals are very magnesian, with XMg between 0.78 and 0.92. Bulk rock analyses suggest that precursors to the sapphirine-bearing rocks were igneous cumulates of plagioclase + olivine + hornblende + spinel. Up to 16wt% CaO does not inhibit sapphirine formation and it is the unusually Mg-rich nature of the host rocks which allows sapphirine development. The early igneous assemblage was replaced by one of cpx + sa + hb +± plag at a pressure of 9 ± 1 kbar and temperatures of 900 ± 50°C. Subsequent rapid uplift caused the instability of gt, gt + hb, hb and sa + cpx to form opx + plag ± sp ± sa symplectites. |
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| Keywords: | Key-words: granulite facies Ivrea Zone sapphirine symplectite |
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